Rigidly guided implant placement

ABSTRACT

A system for guiding an implant to an optimal placement within a patient includes a trajectory guide for guiding instruments along a selected trajectory and a trajectory fixation device for fixing the trajectory guide in a selected position. The trajectory guide defines a path configured to align with the selected trajectory. A movable support mounts the trajectory guide and selectively moves the trajectory guide to align the trajectory guide with the selected trajectory prior to fixing the trajectory guide in the selected position. After fixing the trajectory guide, instruments can be inserted along the trajectory through the path defined by the trajectory guide.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/913,178 entitled “RIGIDLY GUIDED IMPLANTPLACEMENT,” filed on Aug. 6, 2004, the contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to spinal fixation devices used inorthopedic surgery. More particularly, the present invention relates toinstrumentation and a method for the optimal placement of surgicalimplements and implants.

BACKGROUND OF THE INVENTION

Spinal fixation systems may be used in orthopedic surgery to align,stabilize and/or fix a desired relationship between adjacent vertebralbodies. Such systems typically include a spinal fixation element, suchas a relatively rigid fixation rod or plate, extending along an axisalong which the vertebral bodies are to be positioned and coupled toadjacent vertebrae by attaching the element to various anchoringdevices, such as hooks, bolts, wires or screws. The spinal fixationelement can have a predetermined contour that has been designedaccording to the properties of the target implantation site and, onceinstalled, the spinal fixation element holds the vertebrae in a desiredspatial relationship, either until desired healing or spinal fusion hasoccurred, or for some longer period of time.

Spinal fixation elements can be anchored to specific portions of thevertebra. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone, whichis the strongest part of the vertebrae. Such screws typically include athreaded shank that is adapted to be threaded into a vertebra, and ahead portion having a spinal fixation element receiving element, which,in spinal rod applications, is usually in the form of a U-shaped slitformed in the head for receiving the rod. In many pedicle screws, thehead is movable and preferably pivotable in all directions, relative tothe shaft. The ability to move the head relative to the anchoringportion of the screw facilitates alignment and seating of a rodconnecting a plurality of screws

A set-screw, plug, cap or similar type of closure mechanism may be usedto lock the rod into the rod-receiving portion of the pedicle screw. Inuse, the shank portion of each screw is then threaded into a vertebra,and once properly positioned, a fixation rod is seated through therod-receiving portion of each screw and the rod may be locked in placeby tightening a cap or similar type of closure mechanism to securelyinterconnect each screw and the fixation rod. Other anchoring devicesinclude hooks and other types of bone screws

Placement of pedicle screws in a percutaneous fashion has becomedesirable for all minimally invasive approaches to the spine. Thistechnique generally relies heavily on a clear understanding of the localanatomy by the surgeon, as well as accurate radiographic guidancetechnology. Generally, placement is done using a large bore needle or acanulated drill to start an initial hole for screw placement. Pediclescrews are preferably threaded in alignment with the pedicle axis andinserted along a trajectory that is determined prior to insertion of thescrews. Misalignment of the pedicle screws during insertion can causethe screw body or its threads to break through the vertebral cortex andbe in danger of striking surrounding nerve roots. A variety ofundesirable symptoms can easily arise when the screws make contact withnerves after breaking outside the pedicle cortex, including droppedfoot, neurological lesions, sensory deficits, or pain.

The placement of pedicle screws and other implants requires a highdegree of accuracy and precision to ensure a proper trajectory for theimplant. It is preferable that each instrument used in the process beinserted along the same trajectory to ensure proper placement. Knownsurgical procedures for inserting pedicle screws involve recognizinglandmarks along the spinal column for purposes of locating optimal screwhole entry points, approximating screw hole trajectories, and estimatingproper screw hole depth. Generally, large amounts of fluoroscopy arerequired to determine a proper pedicle screw trajectory and to monitorthe advancement of a pedicle screws through the vertebra. However,prolonged radiation exposure to a patient and a surgeon is undesirable.

More technologically advanced systems such as the StealthStation™Treatment Guidance System, the FluoroNav™ Virtual Fluoroscopy System(both available from Medtronic Sofamor Danek), and related systems, seekto overcome the need for surgeons to approximate landmarks, angles, andtrajectories, by assisting the surgeons in determining proper tap holestarting points, trajectories, and depths. However, these systems areextremely expensive, require significant training, are cumbersome inoperation, are difficult to maintain, and are not cost effective formany hospitals.

U.S. Pat. No. 6,725,080 describes an image-guided surgical navigationsystem including a tool guide that uses a trackable marker. The surgeonmust manually position of the tool guide and maintain the position ofthe tool guide during surgery through the use of image guidance andcomputer software. Therefore, the position of the tool guide is subjectto human error, fatigue and slippage, and requires continued operationof expensive equipment and prolonged exposure to radiation to maintain.

SUMMARY OF THE INVENTION

The present invention provides a system and method for guiding animplant to an optimal placement within a patient. The system includes atrajectory guide for guiding and restricting instruments along aselected trajectory and a trajectory fixation device for fixing thetrajectory guide in a selected position relative to the patient. Amovable support mounts the trajectory guide and selectively moves thetrajectory guide to align the trajectory guide with the selectedtrajectory prior to fixing the trajectory guide in the selectedposition.

According to a first aspect of the invention, a guidance system for usewhile inserting an implant is provided. The guidance system comprises atrajectory guide defining a path configured to align with a trajectoryfor guiding instruments along the trajectory and a lock for locking thetrajectory guide in a selected orientation relative to a patient. Thetrajectory guide restricts the instruments to movement along thetrajectory.

According to another aspect of the invention, a method for guiding animplant comprises the steps of determining a suitable trajectory forinserting the implant and fixing the trajectory relative to a patientusing a trajectory guide. The trajectory guide is fixed at a fixationpoint located outside the body of the patient.

According to still another aspect, a method of inserting a pedicle screwinto a pedicle bone of a patient is provided. The method comprises thesteps of aligning a channel of a trajectory guide with a pedicle screwtrajectory, locking the trajectory guide in an aligned position,inserting a first instrument through the trajectory guide to create ahole in the pedicle bone aligned with the pedicle screw trajectory, andinserting a pedicle screw through the trajectory guide and into thehole.

In yet another aspect of the invention, a surgical kit for inserting animplant is provided. The surgical kit comprises a first instrument forpreparing a surgical site to receive the implant, a second instrumentfor inserting the implant in prepared surgical site and a trajectoryguide for guiding said first instrument and second instrument along atrajectory. The first instrument and the second instrument are sized andconfigured to fit the trajectory guide.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully understood by reference to the following detailed descriptionin conjunction with the attached drawings in which like referencenumerals refer to like elements through the different views. Thedrawings illustrate principals of the invention and, although not toscale, show relative dimensions.

FIG. 1 illustrates a guidance system for guiding instruments used in amedical procedure according to an illustrative embodiment of theinvention.

FIG. 2 is a detailed view of the trajectory guide of FIG. 1.

FIG. 3 is a side view of a cannula used in the trajectory guide of FIGS.1 and 2

FIG. 4A illustrates a guidance system including a laser unit to assistin identifying a suitable trajectory according to an embodiment of theinvention.

FIG. 4B is a detailed view of the trajectory guide of the system of FIG.4A.

FIG. 5A illustrates a guidance system including an image guided surgeryunit to assist in identifying a suitable trajectory according to anembodiment of the invention.

FIG. 5B is a detailed view of the trajectory guide of the system of FIG.5A.

FIG. 6A illustrates a guidance system having a trajectory guideincluding a track according to an embodiment of the invention.

FIG. 6B is a detailed view of the trajectory guide of FIG. 6A.

FIG. 7 illustrates a flexible arm suitable for use with the guidancesystem of FIG. 1 according to another embodiment of the invention.

FIG. 8 is a flow chart diagraming the steps involved in using theguidance system of FIG. 1 to guide instruments and implants into aselected surgical site along a suitable trajectory.

FIG. 9 is a flow chart diagraming the steps involved in using theguidance system of FIG. 1 prepare a pedicle and insert a pedicle screwalong a trajectory.

FIGS. 10A-10H illustrate the pedicle region during the steps shown inFIG. 9.

DETAILED DESCRIPTION

The present invention provides an improved guidance system and methodfor guiding an implant, such as a pedicle screw, along a predeterminedtrajectory. The present invention will be described below relative to anillustrative embodiment. Those skilled in the art will appreciate thatthe present invention may be implemented in a number of differentapplications and embodiments and is not specifically limited in itsapplication to the particular embodiments depicted herein.

The guidance system of an illustrative embodiment of the invention isused to insert a pedicle screw into a vertebra, though one skilled inthe art will recognize that the invention can be used to place anysuitable implant that requires a known trajectory. Examples of surgicalprocedures suitable for employing the guidance system of the presentinvention include, but are not limited to, insertion of interbody fusiondevices, bone anchors, fixation devices, including rods, plates andcables, artificial disks and hip stems. The guidance system can be usedto position any suitable implant, instrument and/or other device in anysuitable procedure where guidance of the implant, instrument and/ordevice is key.

Referring to FIG. 1, a guidance system 100 of an illustrative embodimentof the invention facilitates placement of an implant, such as a pediclescrew, in a patient while minimizing radiation exposure. The guidancesystem 100 includes a trajectory guide 40 for guiding instruments usedin performing a medical procedure into a surgical site along a selectedtrajectory and restricting the degree of motion of the instruments tomovement along the selected trajectory. An imaging system 20,illustrated as a fluoroscopy unit 21, is provided for initially locatinga suitable trajectory for the instruments used in performing a medicalprocedure, for example, instruments used to prepare an implant siteand/or inserting an implant into the implant site. The system 100 mayinclude an operating table 10 for positioning a patient 14 in a proneposition to expose the surgical site 12 to the imaging system 20 andtrajectory guide 40. As shown, the trajectory guide 40 is positionedoutside of the patient's body.

Examples of instruments used to prepare an implant site and/or place animplant into a surgical site include, but are not limited to awls, bonetaps, obturators, drills, guide wires and implants, such as screws,fusion devices, artificial disks and hip stems. One skilled in the artwill recognize that the trajectory guide 40 is not limited to use withinstruments used to prepare an implant site and/or place an implant intoa surgical site and that the trajectory guide can be used to guide anysuitable instrument used in a medical procedure along a selectedtrajectory.

The trajectory guide 40 can be any suitable device defining a path forguiding a surgical instrument, device and/or implant. The illustrativetrajectory guide 40 includes a cannula 46 defining a path therethroughconfigured to align with the trajectory, though one skilled in the artwill recognize that any suitable guide means may be used. The trajectoryguide can have any suitable cross-section and is not limited to thecylindrical cross-section shown in the illustrative embodiments. Thetrajectory guide can be open or closed to define an open or closed paththerethrough.

The cannula 46 can be spaced from or directly interface with thesurgical site 12. The path through the cannula 46 forms a workingchannel configured to receive and guide selected surgical instrumentsalong the longitudinal axis thereof. The cannula 46 preferably preventsthe instruments from moving in any direction other than along thetrajectory. The trajectory guide 40 further includes a movable guidesupport for moving the cannula 46 into a selected position relative tothe patient in alignment with the trajectory and selectively locking thealigned cannula 46 in the selected position. The movable guide supportincludes a clamp 44 for holding the cannula 46 coupled to a distal endof a flexible arm 42 capable of selectively moving the clamp 44 in threedimensions to align the cannula 46 with a selected trajectory. A joint48 may be provided for connecting the clamp 44 to the arm 42. FIG. 2 isa detailed view of the distal end of the trajectory guide 40 in thevicinity of the surgical opening 12 for the implant site on the patient.The flexible arm 42 allows the surgeon to bring the cannula 46 into thevicinity of the surgical site, while the joint 48 allows for fine-tuningof the orientation of the cannula 46.

The flexible arm 42 can comprise any suitable device for controlling theposition and orientation of the trajectory guide 40 relative to thepatient. As shown in FIG. 1, the flexible arm 42 comprises plurality ofsegments 42 a, 42 b, 42 c pivotally connected together and mounted to astand (not shown), the operating table 10, or other stable support. Thefirst segment 42 a is movably coupled to and slideably relative to afixed shaft 42 d though any suitable means, to allow the flexible arm tomove along a vertical axis to raise or lower the flexible arm 42relative to the operating table 10. The second segment 42 b is pivotallycoupled to the first segment 42 a to provide a second degree of motion,while the third segment 42 c is pivotally coupled to the second segment42 b to provide a third degree of motion. The clamp 44 and joint 48cooperate to movably mount the cannula 46 or other suitable guide to theend of the third segment 42 c. The use of a plurality of movablyconnected segments allows for the surgeon to move the cannula 46 inthree dimensions. The flexible arm brings the trajectory guide intovicinity of an opening in the patient, while the joint 48 allows thesurgeon to accurately position the cannula 46 at a selected anglerelative to the patient.

Referring back to FIG. 2, according to an illustrative embodiment, thejoint 48 is disposed at the distal end of the flexible arm 42 andcomprises a ball joint having a wide degree of motion for orienting thecannula 46, though one skilled in the art will recognize that anysuitable means for connecting the cannula to a movable support systemmay be used. The illustrative ball joint 48 provides a 160° cone ofmotion for positioning the cannula, though one skilled in the art willrecognize that the ball joint 48 can have any suitable range of motion.

The clamp 44 extends from the ball joint 48 for holding the cannula in aselected position, as determined by the ball joint 48 and flexible arm42. The clamp 44 can have any suitable size and configuration forrigidly holding the cannula 46 relative to the joint 48. The clamp 44allows for the position of the trajectory to be fixed at a fixationpoint outside the body, rather than securing the trajectory guide at alocation within the body by, for example, securing the trajectory guideto a body part. The use of an external fixation point facilitatespositioning of the trajectory guide by the surgeon, while reducing therisk of infection to the patient.

The guidance system 100 further includes a least one cannula lock forlocking the trajectory guide in a selected orientation relative to thepatient. After a surgeon positions the cannula 46 in a selectedorientation, such that a path through the cannula aligns with apreviously determined trajectory, a lock or a series of locks associatedwith the movable guide support fixes the position of the cannula 46 tolock the trajectory. For example, the cannula lock can include at leastone arm lock 50 and a joint lock 52. The arm lock 50, which can comprisea plurality of locks, each associated with an interface between twosegments of the flexible arm 42, locks the flexible arm 42 in a selectedposition to secure the segments 42 a, 42 b, 42 c, 42 d relative to eachother. The joint lock 52, when actuated, locks the joint 48 to thedistal end of the third segment 42 c to fix the cannula 46 relative tothe flexible arm 42. The surgeon can manually actuate the cannula lockor automatically actuate the cannula lock to fix the position of thecannula 46 relative to the surgical site through any suitable means.

The locking mechanisms for the arm lock 50 and the joint lock 52 cancomprise any suitable locking mechanism known in the art. Examples ofsuitable types of locking mechanisms include pneumatic locks, mechanicallocks, such as set screws, clamps, collets and friction locks,electronic locks, magnetic locks, electromechanical locks, such aselectromechanical locks utilizing a solenoid mechanism, and others knownin the art.

FIG. 3 is a side view of an embodiment of a cannula 46 for guidinginstruments according to an embodiment of the invention. In theembodiment shown in FIGS. 1 and 2, the cannula 46 comprises a hollowtubular body suitable for insertion in and/or placement adjacent to apatient's body. The cannula 46 has at least one hollow channel or lumendefining a path extending from an open first end 46 a of the cannula 46to an open second end 46 b of the cannula 46 b. The cannula 46 can beformed of any suitable surgical material, such as, but not limited to,surgical stainless steel.

The tubular body 46 can be rigid, semi-rigid or flexible, and can haveany suitable size, shape and configuration suitable for defining atrajectory for implant placement. In the illustrative embodiment, thecannula 46 is straight to define a straight trajectory. Alternatively,the cannula 46 can be curved or have any other suitable shape to definea curved or otherwise shaped trajectory. The cannula 46 is not limitedto a tubular structure having closed sidewalls and can be any componentthat defines a path, including an open channel or a solid member.

As shown in FIG. 3, the second end 46 b of the cannula 46 can beconfigured to interface with bone or another feature to facilitatepositioning of the cannula 46 along a suitable trajectory relative tothe surgical site. As shown, the cannula 46 can include teeth 460 formedon an outer surface of the lower end for engaging the pedicle bone.

The cannula 46 can have any suitable diameter suitable for guiding aninstrument along a path defined by the cannula. According to oneembodiment, the cannula 46 can be configured to receive an instrumentwithin the channel. In this embodiment, the inner diameter of thecannula 46 is slightly larger than the outer diameter of the instrumentguided by the cannula, so that the instrument can be inserted throughthe cannula while the side walls of the cannula maintain the instrumentat a predetermined angle relative to the patient. Alternatively, aninstrument to be guided by the cannula is configured to slide over thecannula 46, with the cannula 46 maintaining the orientation of theinstrument as the instrument slides relative to the cannula. In thisembodiment, the cannula 46 can have an outer diameter that is slightlyless than an inner diameter of an instrument. One skilled in the artwill recognize that the cannula 46 can have any suitable size andconfiguration for guiding an instrument along a selected trajectory.

In one embodiment, the cannula 46 includes one or more stops (not shown)for limiting the insertion depth of an instrument guided through thecannula 46. Each stop is configured to abut a corresponding protrusionor other feature on the instrument to prevent the instrument from movingpast the stop, thereby limiting the insertion depth of the instrument.

The imaging system 20 can comprise any suitable means for identifying asuitable trajectory for surgery and is not limited to a fluoroscopy unit21. According to one embodiment, shown in FIGS. 4A and 4B, thefluoroscopy unit 21 can include a laser unit 22 for producing a lightbeam 24, for example, a focused light beam, for marking the trajectoryafter the fluoroscopy unit 21 identifies a suitable trajectory. As shownin FIG. 4B, the light beam 24 aligns with and extends through thecannula 46 when the cannula channel aligns with the trajectory. Anorientation marker 240, configured to be inserted in the cannula 46,facilitates alignment of the light beam 24 with the path through thecannula 46. The orientation marker 240 can include one or moreradiopaque portions 241, visible using fluoroscopy, to facilitatealignment.

According to the illustrative embodiment, the laser unit 22 for markinga trajectory comprises a Dual Radiation Targeting System (DRTS™)Platform system available from MinRad, Inc. of Buffalo, N.Y. Suitablesystems for using a laser to identify a trajectory are described in U.S.Pat. Nos. 6,096,049, 5,810,841, 5,644,616 and 5,212,720, which areherein incorporated by reference in their entirety.

One skilled in the art will recognize that any suitable light source maybe used to produce the light beam 23 and that the invention is notlimited to a laser unit. For example, the imaging system 20 can employan infrared light source, an incandescent light source or any suitablelight source capable of producing a light beam marking a trajectory.

In another embodiment of the invention, as shown in FIGS. 5A and 5B, theimaging system 20 comprises an image-guided surgery unit 26. As shown inFIG. 5B, the guidance system 100 can include a 3-D array reference 28 tofacilitate identification of a suitable trajectory. The 3-D arrayreference 28 is coupled to a proximal end 46 a of the cannula 46 andcooperates with the image-guided surgery unit 26 to identify a suitabletrajectory for implant placement and align the cannula 46 with thetrajectory.

In one embodiment, the imaging system 20 employs the VectorVision®navigation system by BrainLab AG of Heimstetten Germany, which providessimultaneous navigation in CT and fluoroscopic images during surgery.

According to one embodiment of the invention, as shown in FIGS. 6A and6B, the trajectory guide 40 can include a track 41 configured to receivea clamp 44′ connected to a cannula or an annular ring 46′ defining thepath for the instruments. In the embodiment shown in FIGS. 6A and 6B,the annular ring 46′ holds a screw driver 400 in alignment with aselected trajectory. The annular ring 46′ traverses the track 41, whichallows the annular ring 46′ to move along the trajectory after thetrajectory guide fixes the trajectory by fixing the track 41 in aselected orientation. The user can move the instrument along thetrajectory towards or away from pedicle, while the track maintainsangular and spatial orientation of the instrument. The annular ring 46′and track 41 can allow instruments inserted therein to rotate on a fixedaxis, facilitating insertion of an implant along the trajectory. Oneskilled in the art will recognize that any suitable means for moving thetrajectory guide 40 along the trajectory may be used.

FIG. 7 illustrates another embodiment of a flexible arm 42′ suitable foruse in the guidance system 100 of the present invention. The flexiblearm 42′ includes a plurality of movably linked segments 420 a, 420 b . .. 420 z and a base 421 attached to the operating table. The flexible arm42′ includes a lock, illustrated as a three-lobed knob 520 locatedbetween the series 420 of linked segments and a joint segment 422, forlocking the arm 42′ and associated trajectory guide 40 in a selectedposition and orientation. The illustrative arm 42′ “locks” down theseries of linked segments 420 and the joint segment 422 when the knob520 is turned clockwise. As the user turns the knob, the knob applies aforce to rods located within the series of linked segments and the jointsegment 422 to create an interference or friction fit at the jointbetween the series of linked segments and the joint segment 422. As theknob turns, the joint located at the knob is clamped tight by creating ahigh degree of friction between the two pieces. These friction fitsimmobilize all the linked segments to create a rigid arm. Turning theknob counter clockwise releases pressure induced on all the surfacesallowing the arm to become “flexible” again.

The flexible arm 42′ illustrated in FIG. 7 is available from Mediflex®Surgical Products of Islandia, N.Y., though one skilled in the art willrecognize that the flexible arm can have any suitable configuration,size and source.

FIG. 8 is a flow chart diagraming the steps involved in using theguidance system 100 of FIG. 1 to guide instruments and implants into aselected surgical site along a suitable trajectory with minimalradiation exposure. The illustrative guidance system 100 and methodprovide reproducible, simplified steps for accurately placing an implantin a patient.

In step 810, a surgeon first determines a suitable trajectory for animplant. The step of determining a trajectory involves identifying apotential orientation, i.e., the location and angle, of a surgicalimplant site, such as a pedicle, using any suitable technique. Examplesof suitable techniques for determining a suitable trajectory includeusing a k-wire, fluoroscopy, MRI, laser navigation and image guidedsurgery. For example, a surgeon generally identifies a trajectory byplacing a patient on the operating table 10 in a selected position,locating anatomical landmarks on the patient, for example, usingfluoroscopy, and locating a suitable incision site over the disc spaceof the patient. One skilled in the art will recognize that any suitabledevice and/or method for determining a suitable trajectory may be used.

After determining a suitable trajectory in step 810, the surgeon canmark the trajectory using an orientation marker in step 820. Examples ofsuitable orientation markers include, but are not limited to, a laser, aneedle, an awl and an obturator.

After marking the orientation, the surgeon aligns the trajectory guide40 with the trajectory in step 830. According to the illustrativeembodiment, the surgeon aligns the trajectory guide by first bringingthe cannula 46 into the vicinity of the surgical site and the trajectoryto the surgical site by moving the flexible arm 42 along one or moresuitable axes. The user then moves the cannula relative to the flexiblearm 42 until a path through the cannula 46 aligns with the trajectoryand the cannula 46 defines the trajectory. In this step, the surgeonuses the orientation marker as a guide for alignment of the trajectoryguide path with the trajectory defined in step 810. For example, thesurgeon can place the cannula over the orientation marker to align thecannula with the trajectory.

After alignment, the surgeon rigidly fixes the aligned trajectory guidein the selected position, orientation and angle relative to the surgicalsite in step 840 so as to define a fixed, guided trajectory for theinstruments used in inserting instruments for the implant and theimplant itself.

After fixing the trajectory, the surgeon removes the orientation markerin step 850, leaving the trajectory guide in the selected positionaligned with the trajectory.

In step 860, the surgeon guides an instrument along the trajectory usingthe fixed trajectory guide. The use of a fixed trajectory guide definingthe trajectory allows the surgeon to guide the instruments along thespecified trajectory without requiring fluoroscopy. In step 870, theuser uses the instrument, as guided by the trajectory guide, to performmedical procedure, for example, to prepare the surgical site and/or toinsert the implant along the trajectory. The user can repeat steps 860and 870 using different instruments as necessary to perform the selectedmedical procedure. The trajectory guide, which remains fixed, ensuresthat each instrument travel along the same trajectory.

FIG. 9 illustrates the steps involved in preparing a pedicle andinserting a pedicle screw into the prepared pedicle using the guidancesystem 100 of the illustrative embodiment of the invention. Theillustrative method ensures proper pedicle screw placement with minimalradiation exposure. FIGS. 10A-10H illustrate the surgical site duringeach of the respective steps of FIG. 9. As shown, throughout theprocess, a trajectory guide maintains a trajectory T-T for guiding thepedicle instruments and the pedicle screw into the surgical site.

After identifying a suitable trajectory and marking the trajectory usinga laser beam that intersects extends from the incision point of thepatient, the surgeon, in step 910, connects a flexible arm 42 to apreparation cannula 46 via a clamp 44 and moves the assembly into thevicinity of the surgical site 12, as shown in FIG. 10A. The preparationcannula 46 guides instruments used to prepare the pedicle 120 forreceiving a pedicle screw. Preferably, the incision point for a pediclescrew trajectory is at the junction of the pars interarticularis, thesuperior articular facet and the transverse process, though one skilledin the art will recognize that any suitable location can be used as theincision point.

In step 920, the surgeon aligns the cannula 46 with the trajectory usinga first instrument. The surgeon aligns the cannula 46 by guiding anobturator/awl 82 through the cannula 46 to the incision point, such thatthe tip 82 a of the instrument touches the laser dot produced by thelaser at the incision point. Then, the surgeon aligns the cannula 46with the laser beam. As shown in FIG. 10B, the illustrativeobturator/awl 82 includes a pointed tip 82 a suitable for punchingthrough the cortical wall of the patient to create a path, aligned withthe trajectory, down the muscle plane to the facet. Alternatively, thesurgeon inserts the obturator/awl 82 prior to moving the assemblytowards the surgical site, then aligns the cannula using the point 82 aof the obturator/awl 82.

In step 930, the surgeon continues to guide the first instrument,illustrated as the obturator/awl 82, through the aligned cannula untilthe tip 82 a punches through cortical wall to begin the incision.

In step 940, while maintaining the obturator/awl 82 in alignment withthe laser, the surgeon advances the cannula 46 over the obturator/awl 82towards the surgical site, as shown in FIG. 10C. In the illustrativeembodiment, the surgeon advances the cannula until the teeth 460 formedon the distal end of the cannula engage the vertebral facet.

Alternatively, the surgeon first punches through the cortical wall usingthe obturator/awl separate from the cannula 46, aligns the obturatorwith the trajectory using the laser and slides the cannula 46 over thealigned obturator to align the cannula 46 and create the initialincision at the surgical site.

After assuring that the cannula 46 is still aligned with the laser andmaking proper adjustments, if necessary, the surgeon locks the flexiblearm 42 to fix the position of the cannula 46 relative to the surgicalsite in step 950.

In step 960, the surgeon removes the obturator/awl 82, leaving thecannula 46 in the selected orientation, as shown in FIG. 10D.

In an optional step 970, the surgeon inserts a drill or probe throughthe cannula 46 to drill or probe a hole along the trajectory through thecenter of the pedicle. The drill or probe is sized and configured to fitthe path defined through the cannula 46, and advance along thetrajectory, guided by the cannula. The close fit between the cannula andthe instrument prevents the instrument from deviating from thetrajectory.

In step 980, the surgeon performs a bone tap using the cannula 46 toguide the path of the bone tap instrument used to perform the bone tap.To perform the bone tap, the surgeon inserts a bone tap 84 through thecannula 46, as shown in FIG. 10E, taps the pedicle and removes the tapfrom the cannula. During the bone tap, the cannula 46 constrains themotion of the bone tap 84 along the trajectory, preventing the bone tapfrom removing bone that outside of the trajectory.

In step 990, the surgeon replaces the preparation cannula 46 with alarger insertion cannula used to insert a pedicle screw along thetrajectory while holding back the tissue in the vicinity of theinsertion site. As shown in FIGS. 10E-10H, the surgeon replaces thecannula 46 by sliding the C-shaped insertion cannula 46′ over thecannula 46, as shown in FIG. 10F, and securing insertion cannula teeth862 to the transverse process, as shown in FIG. 10G. While the cannula46 maintains the position of the insertion cannula 46′ in alignment withthe trajectory, the user detaches the cannula 46 from the clamp 44 andattaches the clamp 44 to an attachment site 861 on the insertion cannula46′. If necessary, the surgeon recalibrates the trajectory. Then, theuser removes the cannula 46, leaving the insertion cannula 46′ definingthe trajectory T-T, as shown in FIG. 10H.

The insertion cannula 46′ has a larger diameter than the cannula 46,suitable for dilating and retracting the tissue in the vicinity of theinsertion site, which further opens and exposes the surgical site tofacilitate insertion of a pedicle screw.

Finally, in step 998, surgeon inserts a pedicle screw through theinsertion cannula 46′, as shown in FIG. 10H, such that the pedicle screwaligns with the trajectory. The surgeon inserts the pedicle screw byinserting the stem of a pedicle screw through the incision site made instep 930 and into the hole defined by the bone tap in step 980. Using ascrewdriver inserted through the insertion cannula 46′, the surgeon thensecures the pedicle screw to the pedicle.

According to an alternate embodiment, the preparation cannula 46 is usedto both prepare the pedicle and insert the pedicle screw without using atissue retractor.

The guidance system 100 can include a single uniformly sized cannulasized and dimensioned to receive and guide all instruments used inpreparing a pedicle and inserting a screw into the pedicle along atrajectory. For example, all instruments used in the preparation andinsertion process can have an outer diameter approximately equal to theinner diameter of the cannula. Alternatively, the guidance system 100can include a plurality of cannulas, each sized and dimensioned toreceive and guide a selected subset of instruments. For example, a firstcannula, i.e., a pedicle preparation cannula, can be sized andconfigured to receive and guide a first subset of instruments used inthe pedicle preparation process, such as the probe, drill and tap. Asecond cannula, i.e., a screw insertion cannula, can be sized anddimensioned to receive and guide a second subset of instruments, forexample, the screw driver, used to insert a screw into the pedicle. Inanother embodiment, a guidance system includes only a pedicle prepcannula, allowing the surgeon to subsequently insert the screw withoutguidance.

According to another embodiment of the invention, the process ofpreparing for and inserting a pedicle screw can omit the step of tappingthe bone in step 980 when the cannula 46 is used to insert self-tappingpedicle screws. In this embodiment, the surgeon defines a suitabletrajectory, aligns the cannula with the trajectory and secures thecannula 46 in a fixed orientation in alignment with the trajectory, asdescribed above. Then, the surgeon inserts a self-tapping screw alongthe trajectory under the guidance of the cannula 46 sized and shaped toreceive and guide a screwdriver for screwing the self-tapping screw inplace.

Those skilled in the art should recognize that there are many differenttypes of cannulas and many different ways in which cannulas could beused. For example, a cannula could be rigid, semi-rigid, or flexible andcould be configured in any number of different forms, such as acatheter, needle, endoscope, implement inserter, etc.

The use of a rigid lock for locking a trajectory guide into a selectedposition aligned with a suitable trajectory provides significantadvantages over prior systems and methods for guiding instruments duringa medical procedure. By maintaining the trajectory guide position with arigid arm, image guidance is not required and therefore, the guidesystem does not require the continued use of a tracking marker afterinitial alignment of the trajectory guide with the cannula. Once thetrajectory has been determined, the tracking marker is no longer usedwhile guiding instruments to the working space. The use of a rigidlyfixed cannula further eliminates the need for guide wires to maintain aselected trajectory, which tend to advance in the patient, causinginjury, and are not as accurate.

The present invention has been described relative to an illustrativeembodiment. Since certain changes may be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

The invention claimed is:
 1. A method for guiding a pedicle screw for apatient having a body, comprising the steps of: determining a suitabletrajectory for inserting the pedicle screw into a pedicle of thepatient; fixing the trajectory relative to a patient using a trajectoryguide, wherein the trajectory guide is fixed at a fixation point outsidethe body of the patient, wherein fixing the trajectory comprises:positioning a flexible arm relative to the patient, wherein the flexiblearm has a plurality of segments that are pivotally connected by joints,including at least one ball joint; fixing a position of the flexible armby locking the joints of the flexible so that the joints will not pivotfrom their current positions; holding a cannula in a clamp that iscoupled to the flexible arm, wherein the cannula serves as thetrajectory guide for the trajectory; and locking a position of thecannula relative to the flexible arm via a cannula lock when the cannulais properly positioned to be aligned along the trajectory; and passingthe pedicle screw through the cannula so that the pedicle screw may beimplanted into the pedicle of the patient.
 2. The method of claim 1,further comprising the step of inserting an instrument along thetrajectory using the trajectory guide, wherein the trajectory guideconstrains the movement of instrument along the trajectory.
 3. Themethod of claim 1, wherein said determining a suitable trajectorycomprises one of using a guide wire, using a laser, using a fluoroscopyunit, using an image-guided surgery unit and combinations thereof. 4.The method of claim 1, further comprising the step of aligning thetrajectory guide with the trajectory prior to said fixing.
 5. The methodof claim 4, wherein the step of aligning the trajectory guide comprises:bringing the trajectory guide into a vicinity of a surgical site forreceiving the implant; and moving the trajectory guide until anorientation marker marking the trajectory passes through and aligns witha path extending through the trajectory guide.
 6. The method of claim 1,further comprising moving an instrument along the trajectory byinserting the instrument through the cannula.
 7. The method of claim 6,wherein inserting the instrument comprises inserting the instrument intoa channel of the trajectory guide and moving the channel along thetrajectory using a track.